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Willamette Escarpment

BACKGROUND

Unique Geology and HabitatRising steeply on the east bank of the Willamette River, the Willamette Escarpment is a unique geologic artifact of the Lake Missoula floods from 15,000 years ago. The well-drained, gravelly soils of the south and west facing escarpment landscapes were once covered with Oregon white oak, Pacific madrone, and native grassland habitats.

Pre-Settlement FireFire is a natural part of the Willamette Valley ecosystem. Although few lightening strike fires have occurred in recent history due to changes in the climate, Native Americans learned from observation that burning enhanced many aspects of the landscape. Fires reduced build-up of dead grasses, twigs, and limbs that accumulated on the ground, making way for fresh growth of herbaceous plants and pruned dead twigs and limbs from oaks, maple, and madrone, and enhancing new growth. Before modern settlement in the mid-1800s, Native Americans used fire to favor oak woodlands and grasslands by igniting grass fires that would kill conifer and shrub seedlings keeping them from overtaking oak habitats. These burns enhanced acorn crops, grasses, and other useful plants and kept the landscape fuels low and easily manageable.

Degradation of the EscarpmentPeople have lived along the Willamette’s banks for approximately 10,000 years, but the major alteration and degradation of the river did not begin until European settlement in the mid 1800s. Portland was incorporated as a city in 1851. Logging, land clearing and conversion, and fire suppression began to be regularly practiced here as they were across the country. Trees along the Willamette riverfront were clear-cut and a rectangular grid of buildings took their place. Historic drawings, photos, and survey records from the 1850s document the degradation of the escarpment landscape since the early days of Portland’s settlement. First, logs were cut from the bluffs for steamship fuel and plank roads, then all lands on the banks of the river, except the steepest sloped escarpments, were developed. In many areas, after the last trees were cut, impenetrable thickets of clematis, Scot’s broom, and Himalayan blackberry began to envelop the landscape and the remaining native oaks and other indigenous plants were smothered.

Weeds Fuel FireFire suppression and the profusion of invasive weeds have increased fuels significantly across the landscape. Many non-native, invasive plants have altered fire conditions throughout the West because they produce highly flammable resins or an abundance of dry material on an annual basis, thus increasing the potential frequency of fires. Here in the Willamette Valley, Himalayan blackberry, clematis, and Scot’s broom grow faster; produce more dead and dry plant material; and have more flammable chemicals in their tissues than native plants - traits which have markedly increased fire occurrences.

Reducing Fire Hazard by Restoring Native HabitatFires play a natural and necessary role in the health of forests and grasslands. When fires are routinely suppressed, flammable material can build up and increase the risk of large wildfires that could threaten homes and neighborhoods.

Although planned fire will be used in certain areas to reduce fuels and restore ecosystem health, its use will be limited due to the proximity of homes, steep slopes, and heavy fuel loads that have built up along the Willamette Escarpment over the past 150 years. In most cases, other methods of fuel reduction will be used instead. There are many methods of reducing hazardous wildfire fuels like Himalayan blackberry. Manual cutting, mowing, applying herbicides, and using planned burns are all effective methods of invasive vegetation reduction, which is an essential step towards the restoration of oak woodland and prairie habitats.

Restoring native grassland habitat along the bluffs and basin of Oaks Bottom will reduce fire risk by reducing overall fuels as well as the occurrence of the more flammable invasives. On the bluff slopes, fire risk will be reduced by replacing flammable shrubs and lianas, such as Himalayan blackberry and clematis, with native grasses and shrubs.

Since the mid-1990s, Portland Parks & Recreation (PP&R) and the Bureau of Environmental Services (BES) Watershed Revegetation Program have been managing 180 acres of the escarpment landscape - 40 acres at Oaks Bottom and 140 acres at Mocks Crest - working to restore Oregon oak woodlands and grasslands. Much work remains to be done and the continued buildup of non-native vegetation puts these landscapes at high risk of catastrophic wildfire.

PROJECT FOCUS AREAS AND GOALSThe 75-acre South Escarpment Unit extends from the Sellwood Bridge north to the Ross Island Bridge and includes Oaks Bottom Wildlife Refuge, which is publicly-owned and managed by Portland Parks & Recreation. The wildlife refuge is a focus area for fire reduction projected along the south escarpment unit. The south unit also includes additional State of Oregon and Metro parcels, and several privately-owned properties.

The 200-acre North Escarpment Unit of the escarpment rises abruptly from the east bank of the Fremont Bridge and parallels the river northwest to the St Johns Bridge. This unit is composed of several small degraded PP&R natural areas, referred to as the Willamette Bluffs, which is a focus area for the north unit. It also includes parcels of unmanaged lands currently in the jurisdiction of other City bureaus and the Port of Portland, Waud Bluff on the University of Portland campus, and many privately-owned properties.

Funds from the FEMA Wildfire Risk Reduction Project will be used through April 2009 to reduce highly flammable non-native plants along the Willamette Escarpment, as well as in Powell Butte Nature Park and Forest Park. With consent of property owners, these funds will also allow the City to aid private landowners within the project areas to accomplish similar goals on their property.

In addition, FEMA project funds will be used to plan for the long-term management of the Willamette Escarpment project area by supporting the development of a Desired Future Condition (DFC) plan for each focus area, which will be used to: